During the past year, this multidisciplinary program project on parasitic infections continued studies aiming at elucidating the pathogenic and modulating mechanisms in the following areas: 1. In schistosomiasis, the protective function of the eosinophil within the host granulomatous response surrounding S. mansoni eggs has been defined. In the absence of these cells, eggs accumulate in the host tissues causing considerable morbidity. Studies on S. japonicum infection resulted in understanding the course of pathophysiological modulation and the underlying mechanism of decreased disease in chronically infected mice. Furthermore, the specific glycoprotein S. japonicum egg antigens responsible for sensitization for granuloma formation and elucidation of immediate hypersensitivity have been isolated and characterized. 2. In giardiasis, the dynamics and characteristics of immunity passively transferred from mothers to their offspring have been delineated. These changes were reproduced by injecting sex hormones in female mice. In addition, the localization of the organism and histopathologic changes in the intestines of G. muris infected mice were studied. 3. Immunologic investigations aimed at defining the interaction of macrophages, lymphocytes, serum borne factors and the parasites as they contribute to immune response and its regulation in human and experimental schistosomiasis. Studies were carried out in Egypt and Cleveland to evaluate the suppressor splenic cells, the immune response to worm antigens and monocyte mediated killing of schistosomula in human schistosomiasis. Furthermore, the mechanism of augmented schistosomula killing by activated macrophages have been described.